Atrial septal defects (ASDs) account for 10% of all congenital heart lesions and are commonly diagnosed in adulthood. Closure of these defects is indicated to prevent the development of reduced exercise tolerance, atrial arrhythmias, congestive heart failure, and pulmonary hypertension. Catheter device closure has been in use for 20 years and is as effective as surgery but with less morbidity. Atrial septal defects (ASDs) are among the most common congenital heart defects, with approximately 18% of defects 4 mm or greater requiring intervention. Additionally, natural history studies have shown that ASDs with diameters of 8-10 mm rarely close and usually require intervention. In past years, surgery was the only option for repair of defects with larger diameters, but since the first reported trans-catheter closure of ASD by King in 1976, efforts are leading to the closure of such defects by trans-catheter techniques.
The interventional cardiologist looks at ASDs as either simple or complex. Those simple can be closed easily by conventional devices without complications. However, the complex ones can either end by fixing the defect in the cardiac catheterization laboratory or in the operating room by the surgeon.
The complex ASD anatomy was arbitrarily defined as ASDs with stretched diameters larger than 26 mm with a deficient (<4 mm) rim, two separate ASDs with a distance greater than 7 mm, fenestrated atrial septum or redundant and hypermobile (>10 mm) atrial septum.
Complex anatomy ASD that may require the use of the present invention include:                1. Large ASD secundum        2. Deficient anterosuperior rim ASD        3. Multiple or fenestrated ASD        4. Deficient posteroinferior rim ASD        5. Aneurysmal atrial septum        6. Combination of the aboveLarge Defects:        
One complex anatomy of ASDs is simply the size of the defect even with adequate rims. A large ASD has been defined as an ASD with a stretched diameter>26 mm. A similar definition was used by other workers in this field. Although it seems like a simple problem, the questions would be how large a device could be used to close such a defect, whether or not the left atrium would accommodate such device and whether such a large device would encroach on other intra-cardiac structures (e.g., mitral valve) or obstruct blood flow (e.g., vena cavae or pulmonary veins). As pointed out recently, large defects are likely to be associated with deficient posterior-inferior rim, which makes the device implantation even more difficult.
Deficient Anterosuperior Rim:
A deficient anterosuperior rim is frequently encountered with large ASDs and indeed in our own personal experience most patients we attempt to occlude with various devices were found to have a deficient anterior superior rim. In one study it is the deficient inferior rim that was found to be associated with unsuccessful Amplatzer® implantations. An Amplatzer septal occluder, (AGA Medical Corp, Golden Valley Minn. is a self-centering device that has been successfully used in clinical trials. With deficient anterior rim, the disks of the Amplatzer device straddle the ascending aorta. With other double disk devices the left atrial disk sits on the back of the aorta. Initial reports of erosion of the aortic wall by the ASO with development of aorta-to-right atrium or aorta-to-left atrium fistulae led to the recommendation of over-sizing (i.e. using a device size 4 mm larger than the measured stretched diameter) the implanted device in large defects with deficient anterior superior rim to ensure the device disks straddle and remain flared around the ascending aorta to prevent discrete areas of pressure where erosion may occur. When over-sizing the device, care has to be taken not to interfere with surrounding intra-cardiac structures.
However, the difficulty in deploying the atrial septal occluder ASO in patients with deficient anterior superior rim is that the left atrial disk tends to become perpendicular to the atrial septum leading to prolapse of the left disk into the right atrium, representing a challenging difficulty.
Multiple or Fenestrated Defects.
These represent another complex anatomy of the ASD which may be successfully closed using different techniques or devices. One approach reported the use of balloon atrial septostomy to create a single large defect that could then be closed with a single large ASO device. We are not in favor of using such a technique. Szkutnik et al. reported a technique, which has been used in many institutions and that is using a single ASO device deployed in the larger defect to occlude two or more smaller defects. In their series, a smaller defect less than 7 mm distance from the larger defect had a 100% closure rate at one-month follow-up. Deploying the device in the larger defect may decrease the distance between the two defects or even compress the smaller defect. They found that if the distance between the two defects is >7 mm, a residual left to right shunt will persist.
Deficient Posteroinferior Rim:
Closure of a large ASD with deficient or absent posterio-inferior (PI) rim continues to be a challenge. An insufficient number of cases with deficient PI rims were reported and makes it more difficult to have a solid consensus. Pedra et al. mentioned one case with deficient anterior rim and a floppy, thin and hyper mobile posterior rim that was not a good candidate for device closure. Du et al. reported patients with deficient rims, of which 3 patients had deficient inferior or posterior rims. Two patients had 2 mm of posterior rim and the third had a 4 mm posterior rim. These 3 patients were successfully closed. Yet, the number of cases is too small to make a generalized conclusion. Lack of detailed anatomical description of the deficient rims and surrounding rims and defects in most reported studies adds to difficulty in drawing useful conclusions. Mathewson et al. defined absent PI rim as a rim<3 mm. As the difference in radius length between right and left atrial disks of the ASO is 2-3 mm, a rim<3 mm will not allow both disks to hang on both sides of the rim. They found that defects with absent PI rim tend to be larger in diameter. They concluded that, although a stable ASO deployment is possible, these defects are more liable for complications such as pulmonary vein or IVC obstruction, encroachment onto the anterior mitral leaflet, or frank embolization.
Aneurysmal Atrial Septum:
Septal aneurysms with single or multiple defects represent a different kind of complex anatomy of the ASD. Such anatomy is better dealt with devices that don't rely on stenting mechanism within the defect to achieve stabilization in the septum. Patch or double disc type of devices such as the COD buttoned device, the Helex, the CardioSeal or the more recent Amplatzer cribriform are more appropriate choices to close such defects.
In conclusion, most cases of complex anatomy of secundum atrial septal defects can be closed successfully either by using traditional or special techniques or devices. Defects with deficient or absent posteroinferior rim continue to form a challenging task for most interventional cardiologists.
In essence the problem associated with an Amplatzer septal occluder devices (ASOD) which is the most common technique used to close atrial septal defects is that the cable has limited maneuverability (rotational steerage) inside a heart chamber. This is more obvious in cases of large atrial septal defectes with deficient rims.
The solution is to modify the device so that it can be steered enough to orient the device to be generally parallel to the plane of the atrial septum. Thus, Applicant's have modified the neck (distal segment) of the Amplatzer cable and refer to it as COBRAX because it moves like a cobra snake.
Methods to Prevent Amplatzer Disk Prolapse:
One method suggested to prevent disk prolapse when rim deficiencies or atrial dimensions restrict device orientation is to withdraw a partially deployed device from the mouth of the right upper pulmonary vein, in contact with the posterior superior septum, in an attempt to maintain the device parallel to the atrial septum as it is deployed. This maneuver can avoid rotation of the left atrial disk. Another method that has also been successful is engagement of the left upper pulmonary vein with the left atrial disk and deployment of the right atrial disk. This maneuver relies on induced tension to pull the left atrial disk toward the septum once the right atrial disk is engaged. Another technique is the use of a special braided reinforced sheath with two curves at its end (Hausdorf sheath, Cook, Bloomington, Ind.). The sheath always aligns the left atrial disk parallel to the septum, avoiding prolapse of the disk through the defect. A large experience with this catheter, however, is lacking. However, a disadvantage of the Hausdorf sheath is its bulky shape, making it difficult to maneuver through the inferior vena cava and a small right atrium. After attempting the standard technique of deployment, if prolapse occurred two or three times, then we attempted the right upper pulmonary vein approach followed by the left pulmonary vein approach. Caution is advised when recurrent rotation of the sheath is required, as it may inadvertently unscrew the device. To prevent this, the delivery wire must be rotated with the device. High-resolution fluoroscopic magnification of the junction between the microscrew of the device and the screw in the cable can ensure the connection windings are appropriate with no gap between the two. Excessive manipulation within the left atrium itself may be hazardous with the potential for perforation. The techniques used for closure of large defects are at the high end of the learning curve. Large device implants are feasible with views from ICE when it is essential to have high-quality imaging to position the implant reliably. The use of ICE catheters may improve visualization of the inferior rim compared to TEE. Anew approach with use of a second sheath or sizing balloon to stabilize the inferior aspect of the retention disc while deploying the right atrial disc has been reported as a useful method for complex ASD closures. Yet, these maneuvers necessitate an additional large venous access on the contralateral femoral site, potentially increasing the risk of vascular access complications. Finally, a modified, shortened Mullins-type delivery sheath with a bevel at its inner curvature may facilitate deployment of an ASO in complex, large secundum ASDs with deficient rims. A modified Agilis sheath has also been used to overcome the difficulties in closing complex ASD's.